<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
  * {
    margin: 0;
    padding: 0;
  }
  html, body {
    height: 100vh;
  }
  .content{
      display: flex;
      height: 100vh;
      border-color: red;
  }
  </style>
</head>
<body>
  <div class="content">
    <div class="box1"></div>
    <div class="box2"></div>
  </div>
</body>
</html>